Can we ever know how another person "senses" the
world?

In my Bioelectricity class this week, we learned about the cells
in our body that help us sense our environment: chemosensors in our
tongue that help us sense taste, for example, the photoreceptors in
our eye that sense light, and the hair cells in our ears that sense
the mechanical vibrations of sound, to name a few.

As a result, I recently revisited my answer to the age-old question of
“how do I know that the blue I see is the same blue you see?” that was
so startling and exciting to most 3rd graders playing baby Kierkegaard
a little bit differently. An answer could be that we just have to
trust that perception is guided by biology and that humans are
biologically identical to within 80% of our biological systems.

This answer, of course, raises new questions: even if you and I may
perceive the same blue, is that blue "real?" Where does sensation
leave off and perception begin, and how may we trust ourselves as we
try to compare them? Can we ever know how another person "senses" the
world? Would love to hear your thoughts!

Feb 16 2012:
An interesting facet of this question is the role that emotions play in our perception of the world. Scientific understanding of how this works is still at a basic level, but experiments are showing that a change in emotional state can often affect one's perception. And of course the sense data we receive from the world has to pass through the filter of our attention as well, and this filter is highly sensitive to emotional context. All of this explains why, if we have a strong emotional association with a particular color, taste, smell, sound or texture, we start to observe it more often (and possibly differently) in the world.

So, while I think it's reasonable to argue that our biological apparatus for sensing the world is fairly similar from person to person, that sensing process cannot in practice be decoupled from the processes of attentional filtering and emotional interpretation, which are likely to vary widely between people.

Feb 18 2012:
I believe it is possible to understand how another experiences the world, although perhaps it is mistaken and disrespectful to assume it. Through meditation and reflection, we can come to understand deeply the workings of our mind and how we live through our perceptions. During this process, we may experience something beyond what we live through our limited sense perceptions - presence, awe, joy, the mystery. We may understand that we are all expressions of the universe, of spirit, of God, of love (whichever words we choose to attempt to describe our experience) in a human form. When we are fully living in this awareness, in non-duality, we may be able to see how others are experiencing life. If we spend time or work with people who have this level of awareness, we can easily get freaked out by how easily and quickly they understand us.

I offer you the champion work of Ramachandran on the vexing nature of the human 'senses'. A quick watch will educate and amaze even the least scientifically inclined.

As to your questions, i hope i am addressing correctly..

1. Even with 80% similarity, the sensory issue is based entirely in the brain. In the brain, the no. of possible pathways are more than the no. of subatomic particles in the Universe (as Ramachandran puts it eloquently). Thus, the possibilities are fairly large.. even then, due to specialization (localization of function) in the brain, we can have 'types' of sensory experiences, sort of like constellations rather than merely infinite different experiences.

3. And unfortunately the question of 'blue' is semantically tangled. The question should begin with what is "blue"..? What range of wavelengths constitutes 'blue' for the average human being..? Is the effect on standard human cone-cells equal in all populations..? (A simple look > http://en.wikipedia.org/wiki/Cone_cell ) Is the neural excitation similar on an average for all persons at say 420nm..?

Feb 17 2012:
your comment about the many possible pathways that the brain can form speaks to something else: the way we perceive is consistent (for an individual) -- suggesting that our perceptions are pathways that have been established. our environment surely has an impact on our perception, as rebecca parr pointed out by commenting that we develop depth perception due to our surroundings as well as the development of our brain-- that is that we have developed the ability to perceive depth because depth is a characteristic of the environment that is important to our survival (falling into a cliff, anyone?)

my point: if we accept that our perception is influenced by our environment and its characteristics, it is plausible that peoples living in one terrain or climate would perceive things differently than those in another.

Feb 18 2012:
I agree with you..
I was hoping to address you at what was inquired.

As a matter of fact, this case that you raise, of "(is it) plausible that peoples living in one terrain or climate would perceive things differently than those in another." - is addressed in the third sentence (question) of pt.3 from my comment: "Is the effect on standard human cone-cells equal in all populations..?"
I agree that our perception of reality is fairly consistent, even as a world population; but a simple disorder, like 'color blindness' shows that it isn't easy pinning down 'correct' perception. However, it is possible for us to tell that a person is color blind due to that same consistency of perception thru'out the world population.. i hope i am being lucid here.

This connects to your other sub-point about perception itself - and you can show via statistical methods that you'll have a Gaussian distribution for sensory perception. After all, perceiving things equally is a major evolutionary benefit. Also, think about your depth argument - you agree, that "we develop depth perception due to our surroundings as well as the development of our brain"; however it has a lot to do with stereoscopic vision that most mammals have, they too perceive depth, dogs do it astoundingly well. This is just something that we're left with. Tell me, wouldn't you think that having three eyes, one located at the back of the head would be excellent in protection from predators..? It would be, but we'd never know if there could be some ancestors that we could have with three (or more) eyes who could've led to humans (we know spiders {order: araneae} often have four pairs of eyes). So what stopped us from being in that kind of a branch in the tree of evolution..? Maybe such a mutant line was wiped off early in the tree by nature. Plus, very important is also that we - human beings, were very nearly driven to extinction.. we all come from a group of about few (ca. 10-50K) individuals.

Feb 20 2012:
And as imagination bodies forth
The forms of things unknown, the poet’s pen
Turns them to shapes and gives to airy nothing
A local habitation and a name.
Such tricks hath strong imagination,
That if it would but apprehend some joy,
It comprehends some bringer of that joy.
Or in the night, imagining some fear,
How easy is a bush supposed a bear!

We are all poets - authors of our experiences, and our perceptions - and, yes, in as much as we share a "local habitation and a name" we are, most certainly, likely to perceive things similarly.

Feb 19 2012:
To build on your point, even though the general wiring of the human brain is specified by genetics, a great deal is influenced by nurture. For example, in the visual system, the neurons coming from the lateral geniculate nucleus are mapped to a specific topographic configuration in all individuals, but each cell differentiates so as to handle only signals coming from one eye (ocular dominance columns), and this is unique to every individual.

Not surprisingly, concepts' and qualia's topographic mapping on the brain seem to correspond closely to conscious perception. For example, while continuous wavelengths of light obviously cannot be mapped to a circle, we do perceive colors as on a color wheel, and, indeed, the areas of the brain responsible for color perception are mapped in a circle, even exhibiting a separation between warm colors on one side and cool colors on the other.

I think that since the general mapping is the same in all humans, we are most likely to experience things in much the same way, but because there is inevitable variation from the nurture side of the equation, it is probable that there is, as you say, a kind of "Gaussian distribution of sensory perception," with any possible range of standard deviations.

Feb 19 2012:
After I read Jacques Monod "Change and Necessity" I accepted that nature and human life is not exact but rather a deviation pending around the optimal line... so your "range" explanation is even fitting with a general layout and principles of evolution - at least according to some researchers.

Feb 19 2012:
Must look the book up..
,,for any researcher/scientists who accepts evolution, even in the 'selfish-gene' format, as Dawkins puts it - it is a given consequence of random mutation and genetic mixing that the said 'Gaussian distribution' will arise.

Feb 19 2012:
Totally agree with you, @Simon.
I have much more to read, i see, about what you've stated in your para 2. On it..! And it is precisely due to evolution that we all have inherited a similar general wiring - which in turn results in a similar sensory analysis within the brain.. i think it is very important that we all see things the way almost everyone does; a simple task such as driving would otherwise be impossible (traffic lights, spotting policemen, stop-signs, etc.).
As to your point of nurture, it is extremely important. We form memories via the firing of a specific set of neurons, and this is very very Lamarckian, it is more a horizontal evolution in culture that perceptions shaped thru'. e.g. In say particular culture, purple is considered royal but then a quick look at all the common connotations of Purple will amaze you: "royalty, imperialism, nobility, Lent, Easter, Mardi Gras, episcopacy, upper class, poison, friendship, engineering, passion, sharing, wisdom, rage, homosexuality, contrition, sympathy". [source: Wiki]

Thus, sensory perception is one thing, and reacting to it - another. And on an average we must, due to logical reasons, sense and perceive in similar ways - but since we communicate via body-language and verbal-exchange: the output is always 'colored' (punintended!) by our emotions - as we emote (quite non-objectively) when we respond.

I wanted to answer your question from a more personal perspective especially since it is a question that I have wrestled with for many years. Hopefully it is not too repetitive but I would love to share with you my opinion and how it became so.

“It seems to me I am trying to tell you a dream—making a vain attempt, because no relation of a dream can convey the dream-sensation, that commingling of absurdity, surprise, and bewilderment in a tremor of struggling revolt, that notion of being captured by the incredible which is of the very essence of dreams. . . No, it is impossible; it is impossible to convey the life-sensation of any given epoch of one's existence,—that which makes its truth, its meaning—its subtle and penetrating essence. It is impossible. We live, as we dream—alone. . . ” This quote is from Joseph Conrad’s Heart of Darkness and it has been something that I have taken to heart. No one can relate completely to another’s experiences. No one can articulate one’s emotions in a way that another can feel exactly all that person feels. It has been one of my goals to express myself so that hopefully others can understand and empathize.

Feb 21 2012:
I respect this opinion, and I agree with you. But what if we suspend our disbelief for a moment?...

We can define "sensation" in a number of ways, or at different points along a spectrum, from the very physical (i.e. intensity of heat, light, or sound) to those much less physical (i.e. emotion). It is straightforward to conceive how we might reproduce those sensations that are the most physical (touch your hand to a hot stove to understand heat, look at the sun to understand brightness). Those sensations that are less physical, particularly the ones which are caused by social or cultural situations, must be the hardest to reproduce or understand.

Of course, the following is science fiction, but stay with me...

Consciousness is an emergent property of the firing patterns of our neurons (ok, ok, or God, please no angry comments. I concede, this can be a controversial topic, but that's for another TED thread.) What if each emotion, say happiness, is the result of a given firing pattern, that could be read from one person via either direct neural recordings, EEG, or fMRI, and then directly reproduced in a second person? The connectivity of our nervous systems is unique to each of us (see TED talk I Am My Connectome http://www.youtube.com/watch?v=HA7GwKXfJB0). But since we all feel happy sometimes, perhaps these firing patterns are universal enough that they can be reproduced in most humans.

Now take it one step further. Someone asks you, "How did you feel on the day of your daughter's wedding?" Words cannot describe your feelings. You put on a hat. Take it off. Pass it to your friend. They put it on. "WOW. I am so happy for you," they say.

Feb 18 2012:
I have synesthesia and see color, texture and light mathematically, in 3D. I was an interior designer and great at it, asking each couple and family of clients to wear the colors they Feel best in. None were the same, so finding the overlaps and complimentary colors was key. Then I would ask them to show me fabrics that matched the style, color and feel of what they wanted. Blending all this, I then showed them how different lightbulbs and direct sunlight changed the colors.

Next, I would see what worked for each one of them, where they were harmonious and then go put together 5 choices of colors/fabric/styles in the overlapping areas. When all of them were in agreement, the process was Done and they were all happy, it was like giving them Christmas.

There are so many variables between light perception, color blindness, etc... There are mathematical relationships between colors that are universal, which we see in spirals and fractals, all the time. It's similar. Recognizing them, is the thing. I was trying to develop software to do show the relationships and couldn't get anyone interested in building the data set, to create software to allow everyone to do it.

Feb 17 2012:
Many people here have used the term real, is anything real? we are back to the notion of conciousness and reality once more. Is there a way in which we make sense of the world that we do share with others, if we are in water we all feel resistance, does this mean we sense it in the same way? I'm not sure about that, but we all know that at a certain depth unique to us we find resistance to forward motion provided by the water. Is this correct for everyone?

Feb 17 2012:
Having read about and watched programs on prosthetics(specifically those that interact directly with the nervous system), I have often thought about this. While the first question that comes to mind is "will they see the same world I do?", I have come to the realizations that a)everybody experiences the world differently and b)that as long as long as every bit of information is reaching the brain it doesn't matter if it's the same thing that reaches anyone else's brain.

It's all a matter of language. The brain can learn a new sensory language if it has to, so what u have to do is make sure that any prosthetic has the capability to create "words" for everything. Does the prosthetic eye have different "words" for every hue, shade and tint? Does the prosthetic hand have "words" for soft, firm, hard, smooth, rough, hot to cold? What kind of resolution are they capable of? If u can produce a clean reliable signal then the brain should b able to figure out how to use it on it's own.

@George, when u talk about the relation of tones to each other u put computation b4 perception. Relationships between sounds are not inherent to the sounds, they are a result of the brain creating a relationship between them. Also, our brains do not perceive "white", "grey" or "black" completely without context. What we consider these things to b depends on the relative relationship it has to it's surrounding. The best example of this is how so many things seem white until u put them side by side.

Feb 22 2012:
I don't believe we can precisely know whether we experience the same way as another person . . . at least not so that we can communicate through speaking or writing. However, I believe as we come to understand more about mirror neurons, we will realize that we do not have to experience the exact same thing as someone else to be able to deeply emathize with them. Whether the blue you see is the same shade or different than the one I see, or the sky you see is the same as the one I see, we can find a common understanding that embraces our uniqueness.

Feb 21 2012:
It ought to be trivial to observe that we can only conceive of how others perceive the world in terms of how we perceive it. When an organism has more limited perception than we ourselves do do we feel confident that we can understand that organism's perception. For example, people with good color vision can effectively experience what it is like to see in black and white etc. When faced with types of perception we lack or have poorly we translate it IN TERMS OF OUR OWN PERCEPTION. For example, we have a poor sense of sonar that we complement with vision to imagine how a bat 'sees' the world; we imagine ultra-violet vision in terms of our light vision.

The age-old question of “how do I know that the blue I see is the same blue you see?”contains a flaw. In general we answer the question "Do person A and person B see the same X?" in terms of the real world, and we will use real indicators to verify that they do indeed see the same X. There is no such X as blue. X may be a blue flower and in such a case we may verify that both A and B see a blue flower. Person A can imagine in terms of its perception what B sees and B can imagine in terms of its perception what A sees and we conceive of the whole scenario in terms of our own perception.

The problem is not specifically a color problem. A completely color blind person could wonder if another such person sees the way they do. It is more easily expressed as a color problem because of the color wheel (that is a product of our mechanism of vision).

Our method of answering such questions is through the analysis of mechanism. The extreme cases are:
I see a blue object now in the way I see a blue object now - because the input and mechanisms are identical.
No one sees the blue object in complete darkness - there is no mechanism .

So we assert that similar inputs and mechanisms are a similar kind of perception. And if color wheel translation occurs we would expect it to evident in the mechanism.

Feb 18 2012:
In some measure, you don't need to know --or rather-- it doesn't matter if you know, it simply matters how you act (react/respond) to the 'blue' you see. The role sense play are largely informational, played out in propreoception. Do I say 'blue' when I see 'blue'? Do I reach out and pick up the 'blue glass' without knocking it over? It matters that most of us know to stop when the traffic light turns red, but that behavior might have almost nothing to do with 'color' at a specific wavelength. When perception is translated into action, it has meaning.culturally. Do the thoughts we 'keep' to ourselves, mean anything? Are they effectively meaningful if not accompanied by some interaction with the external environment?

Feb 18 2012:
Semantics but we have a growing understanding of how we sense world.
As to what people are perceiving. Suggest we have a general idea if we share the same senses, similar biology, same physical stimulai - light sound touch etc and similar reference points. Suggest twins might have the closest mutual understanding.

If we see the same picture we may perceive it somewhat differently but there is usually a lot of commonality if people described the scene.

Even someone saying a sentence or humming a tune -we can repeat it back. It might be perceived somewhat differently in each others heads, but for practical purposes there is enough repeat ability in the experience and interpretation and shared symbolism or language to interact in a meaningful way and receive feedback that usually indicates we understand to some extent. We can agree what is blue even if it is perceived differently. In fact language is probably a bigger factor than any difference in perception. In Russian there are two distinct words for lighter or darker blues. When they get close one person might say the darker blue the other the lighter.

Suggest it gets a bit harder when some senses are lacking, and others perhaps others develop to compensate. The world probably seems very different to a blind person.

Recall reading about sensory maps. Obviously most humans have a weight to the visual sense. I guess the world is perceived very different by dogs with a greater sense and weighting towards smell.

Feb 18 2012:
I like the idea of the weighted senses - one more indication that reality as a construction many people have in common and understand it as to be the same is most of all about diversity or change.

reality - if it ever is a same "blue" - is for sure never a stable perception; it is moving - every instance - by all the weighted senses and of course in aging also, since even in an individual person the senses will weigh different with 50 than with 25....

If you think about it:
the strange thing is that communication still works at all - given the diversity and problems of a reality concept....

Feb 20 2012:
I like how you brought up language into this discussion. I think part of the problem of whether or not we all perceive the same thing is that we just can't fully describe what we are feeling. We have ways to describe colors but our ability to fully articulate the depth of a blue we see in the ocean or the richness of a chocolate we indulge on is lacking. We often tend to compare what we perceive to something else more familiar like calling a car the color of the sky. But in that, there lies a fallacy in assuming that everyone else around us perceives the same color blue as we do. Unless our language and ability to completely articulate what we perceive, I do not see how we can truly know how others may see the world. Maybe the idea of weighted senses is how our sense actually work. Or maybe there actually is a standard way of perceiving the world that we just have not been able to analyze yet.

Feb 17 2012:
We can all perceive the same or different blue. We can all feel differently about that particular blue that our senses tell us we see. The depth in perception depends of the amount of input in the subconsciousness, through the consciousness. If you are a person who have seen and perceived many,many different shades of blue, when you see one blue, you'll identify it with the same one you've seen before, so you'll recognize it or, if you see it for the first time, you will first identify it and then record it in your subconsciousness. The next time (or the 50th time) you you'll see that particular blue, you'll just recognize it and you won't see it as a new one. But it is not that important that we can all see different blue, more important is that we all feel some way about some particular blue. Our subconsciousness, without our consciousness knowing, can relate one particular blue with some emotional shock that we've experienced, just because we were feeling something very strong while our senses (our eyes) saw that color. So that is an unwanted relation if the emotion was bad. It exists only untill you become aware of that, of where it all begin. If it was a positive feeling, you'll feel it every time you see that color; you will relate that particular color with happiness etc. So green can trigger pain and fear (of war, of violence) for someone who's father was killed by a solider in green uniform, while for a person who have only good experiences with green, like playing in the park when he was a kid or etc, it might bring feeling of happiness or love. So, more important than the specifying the tone, which is certainly different, is the way a person feels about the color and what he connects it with (when he first perceived that tone, what was happening). And when we got to the feelings, we ALL FEEL LOVE or FEAR THE SAME WAY. EMOTIONS are felt the same. Even they are not triggered by the same situations or thoughts, I feel that we all feel them the same. Are we?

Feb 18 2012:
Hey Marina, your explanation makes a lot of sense to me. I am persuaded that we(considering people who are not colorblind, blind, or with physical ailments) all see the same thing but interpret things differently based on our unique memories of life. After watching the related talk by Nirenberg, about using an encoder-transducer to recreate what the retina was seeing from the firing patterns to the brain, I was convinced the same images are sent to everyone’s retina to be processed. It has to be our stored memories that shape our attitude towards things. The other senses(smell, touch, taste, hearing) probably function in a similar way where memories effect how we interpret things. I also agree that the emotions we feel are the same but may be to different causes.
As for trying to answer the question, I think it is difficult to truly know how another person senses the world. There are different levels of emotions like happiness and sadness. Two people can know the same level of happiness in reaction to some trigger(not necessarily the same for both), but how will they know what the sources were that achieved the same exact feeling? It does not seem possible that somebody can know exactly how happy they are compared with someone else. Perhaps there is an accurate way to measure happiness by the release of some chemical during happiness or increased activity in a particular part of the brain to see if two people actually achieved the same level of happiness.

Feb 20 2012:
I tend to believe that we cannot ever know how another person “senses” the world. Even if we are looking at the same object, or are exposed to the same temperature, for example, each person’s make-up will respond differently to their surroundings. This can be affected by a variety of things. Previous memories or experiences can play a role in what they see, perceive or even feel. There is no defined scale in the human body corresponding to a certain level of emotion or feeling. Our physical as well as our mental interpretations of objects and situations around us make it difficult to be able to compare what we sense, let alone knowing exactly what the other person senses. Maybe as technology progresses we will have better tools to try and know how others “sense” the world, but as of now I see this possible to only a very small extent.

Feb 17 2012:
I'm going with no only because 'sensing' is a biological function and no two humans are alike (not even identical twins), therefore we all sense things differently.

Sure we can have some commonalities in the sensory department like, for example, I suppose we can assume that most of us can feel hot and cold on our skin (barring some medical issue that impedes this, of course) but just how sensitive we are to the cold or the heat can vary--hence we cannot ever fully 'sense' exactly how someone else does.

Feb 17 2012:
I agree with what you say about how everyone is biologically different, but how different are we-- different enough that it would affect our perceptions? and even if we do perceive slightly differently, how would we know? I suggest that maybe the 'error' in the consistency of perception, that is, the differences in our perceptions, are dwarfed by the ambiguousness in how we communicate those perceptions. Basically what I'm trying to say is that the even if we do perceive differently, the differences are so small that they are undetectable or undiscoverable when we try to communicate what we perceive, and to see if we share our perception.

Feb 18 2012:
Fair enough, however your question was about sensory, not about perception; there is a difference. Sensory pertains to the biological responses to stimuli and perception is about our interpretation of that stimuli.

Feb 18 2012:
Hey Estela
thanks for your comments and response. You're reply highlights a common idea that's been coming up in various ways during this conversation, which is that beyond strict sensory perception, going into the realm of interpreting those perceptions is very clearly subjective and very clearly different between any two people.

When we talk about perception though, we are talking about the very basic sensory input-- perception is how humans process (not interpret!) stimuli in the environment-- perception is the immediate result of our senses working. So the question is even more nuanced than 'do we interpret the sensations that we perceive differently'-- it is 'do we even perceive sensations the same way?'

Feb 18 2012:
Hey brigdet,
initially iseemed to agree with your comment (probably because we both found points of argument in Estela's argument), but I have to disagree with one part of what you say-- and don't call mea language stickler!-- but I get wary when the discussion starts to involve the word 'interpretation'.

You talked about the idea of the conscious mind as being the 'center point' in a way of the senses, which is to say that the mind senses stimuli even when the sensory organs (eyes, ears) can't sense. Correct me if that's not what you meant because I had a little trouble understanding what you were trying to say.

But if this is what you meant, again i must disagree, because even in those without blindness, it is never 'the eyes that do the seeing'. The structures in the retina are basically different types of light filters and polarizers, so when the light gets to the very last set of cells of the retina (retinal ganglion cells), that filter light gets transformed into a nerve signal that then causes the brain to see what the eye filtered.

So for people who have blindness but can sense, for example, when an object is thrown at them and then they can duck away ( a seemingly magical thing!), it means that some part of the retina in the eyes are still working, and able to send some information to a part of the brain to tell it to get out of the way-- albeit this is not the part of the brain that can take the signal from the retina and transform that into an image of what is in front of the eye. So in this way the physical eyes are doing the seeing-- its just that the pathways in the brain needed to create vision aren't being taken. The reason I make this clarification iss because I'd like to get away from the idea of consciousness (at least in this context) because it makes it seem that there are intentions/interpretations related to how and what we perceive, which is not the case. (of course interpretation comes in later after we've established to ourselves what

Feb 17 2012:
Two hundred years ago people could not imagine talking to someone who was hundreds of miles away. Today almost everyone does it when they use the phone. People understand that it is possible to communicate sounds over wires that replicate the sounds being made at a long distance. We also understand that those sounds (and images) can be communicated over the airways via radio signals.

The human body communicates within itself via 'wires' know as neurons, but today few people recognize that the body can also communicate both within itself and outside of itself via the airways just like radios do.

For those who have experimented with this they can experience another's sensations and thoughts. This does not come easy and it takes considerable time and effort to develop this ability, so few have ventured into this exploration. Part of this process is developing the ability to stop perception and just allow sensation, which, as you might imagine, if not easy.

Feb 17 2012:
I love to hang out with all of you smart people here. I wish that I was smart enough to comment on this interesting topic. It did make me think about a dog I once had though. I taught Fritz to lay down when I said sit and then to sit when I said lay down. I'd brag how well that Fritz was trained and then do "the bit". Many laughs from many people. He was a good dog and I miss him. Thanks.

Feb 17 2012:
I was thinkging about this a lot when I was around 8-9 years old. I thought "what if what I call yellow, is just yellow for me because my parents teached me its yellow, what if someone see's it in a total different way?".
Now, that I saw this question, this whole thought re-borned in me, and I just realized, it's not important to find out how another person senses the world, but the important thing is that he or she DOES senses the world, and will find the things, thoughts, people, art which will mean something to him or her.

Feb 17 2012:
A few thoughts: (1) some people are colorblind. They certainly don't see the same colors as non-colorblind folks do, or even as other colorblind people do, as there are several forms of colorblindness; (2) the worst witness is an eye witness because h/she doesn't remember or report events accurately. Think "Rashomon." (3) an analogue to the vision question would be taste. People taste the same food differently, and they see the same things differently. Think about a layperson and a radiologist looking at the same x-ray; the latter sees subtleties the former misses; (4) Remember the Chinese chestnut: "There are three ways you are seen--the way you see yourself, the way others see you, and the way you really are."

Feb 16 2012:
I have always loved this question from a young age, and many years later having studied science (biochem) and much later art and film it drove me to look at this from several perspectives. I was fascinated by the philosophical question "Do you see what I see" and also the cultural connotations of different colours,
particulary red - quite fascinating, so global in meaning (is it because blood is red?), and often used as a Motif by filmmakers. I even made a couple of short art films on http://www.youtube.com/user/sparkshorts - RedOrDead and MyFavouriteThings. See what philosophy, science and art can do to our inquisitive minds!? Of course, scientifically the detection of colour is dependent on the sensitity of the three different types of cone receptors in our eyes. If these are different in different people then their range of perception may be different, so one person may effectively be colour blind in comparison to another, or, as in certain kinds of dyslexia, find the contrast between certain colours makes it impossible to discern clear edges so that letters jump around (as most of us find for example for red on green lettering). Sadly with age, we cansee our own perception of colour is slowly draining, as our other faculties, things become less sharp, less intense, sweet roses, fresh lawns, bright beautiful days... But in terms of neural representation of that information internally. Always fascinating. To get inside someone elses brain for just one instance... The other thing which I find fascinating relating to this is the research which has shown that blind people can have the output of small camera's on their foreheads wired to their highly innervated tongues, and then "see" images and reproduce them accurately with a pen on paper as proof of what they see. (In Scientific american published about 2005/6). Surely something very fractal about the way our nervous systems adapt and evolve. But thats another area entirely ....

Feb 16 2012:
You raise an interesting question. I wonder if part of the answer is that the sensation of a color is real if it means something in our perceptions and produces an action. For example, the sensation, "red" on a traffic light results in the perception, "Stop." That's real and results in an action. Interestingly, ultraviolet colors displayed by flowers and tuned over millions of years to the sensation repertoire of honey bees results in attraction to sources of pollen and nectar, and to cross pollination vital—to the survival of plants, bees, and us! We cannot sense the beautiful ultraviolet patterns on blossoms that are "real" to honeybees without instruments to show us those patterns. So, to us, those sensations are unperceived, not real. But honeybees can sense them and they are real, because they lead to a life sustaining perception and action.

Feb 16 2012:
Hi Sophie
I really enjoyed this discussion. Thanks. I wanted to comment to several of the readers, but here I am at the end, and don't want to go back and do it individually. So...
I used to believe as several of the readers said about how our senses work. You know, electrochemical stimuli to the neuron structures etc. etc. From that position, your question is right on the money. If neurons are the creators of our reality, then each individual can sense his own reality. If you could plug your neuron into my cortex you would be aware that my red was your magenta - or what ever.
But I believe that reality is what we are experiencing. Our brain structures - assuming no damage or disease - are creating a common reality to the degree that our genome is similar. Your and my reality is identical. But a deer in the forest sees a different color reality, one that favors a deer's survival. An ant sees another and a bat another. Yet all living things see their own reality within a greater reality, the 'real' reality. If we saw it all we would be deafened by how loud and blinded by how bright it is.
Our living self, our energy life, our soul, if you will, creates the reality that our kind has grown to live in and is reflected within us. What we as individuals experience is as real as it get for any of us, given our differences in genetics. If one of us is a mutant with a different genetic structure which changes the range of electromagnetic spectrum that can be perceived, then he will see a different world than what we see. Any soldier who has used infrared night vision binoculars can verify that. But as far as the rest of us go, given unaltered natural 20-20 vision, what we see is what we all see. Blue is blue, and the blues are sad, and ol' blue will come home when the trumpet shouts his name.

Feb 16 2012:
You make a good point that every organism is evolutionarily tuned to perceive certain things, and to perceive them similarly...

that idea simplifies a lot of the discussion that we've been having about language and how to communicate perceptions, because it transfers the agency of perception from individuals perceiving to evolution/biology sort of...perceiving unto us...

A question that recently popped up in my life that is a response to the original question I posed, and that is:

How do I know that the blue that you and I see is the blue that is actually in front of us? Consider an old CRT tv that was in your grandmother's house, with its wooden frame and tons of static...We know that static (or noise, to scientists) exists everywhere-- in all signals like telephone and tv signals, but also just everywhere in the ambient environment...yet we cannot see that noise and static...

our brains are remarkable at filtering static-- probably better than any noise cancelling technology anywhere, such that we see with amazing precision different objects, wrinkles in peoples faces, colors, etc...we see an image that appears to us to be really clear (if our eyes or glasses are doing their job)

realizing that the brain is so amazing at filtering out noise made me think of what the objects or colors that we look at resemble at all what they look like in 'reality'

Feb 17 2012:
I agree with Seth. A few things I would like to mention in support...

If you read about Autistic savants who have incredible memory, a lot of neural research has shown that the brain has a fiber bundle connected between the two halves whose purpose is to filter stimuli in order for higher level processes. Those savants do not have this bundle, in fact, that part of the brain is fused. They receive the stimuli pure and their higher level parts of the brain has the task of dealing with it, and so most of the stimuli gets stored as if they are important (which is why they have incredible memory). But of course, most cannot function in normal society because they lack this ability to filter stimuli.

Also, have you ever worn individual toed socks? They're very annoying at first, that's because of stimuli overload. When your legs fall asleep is another good example. Because you reduced the bloodflow to the leg, the nerves have to work harder to receive stimuli, the moment blood is reintroduced, the nerve endings are too sensitive.

Feb 17 2012:
The brain doesn't try to model how the world really is as much as it forms associations between past and current experiences in order to determine which behaviour to initiate or maintain, so that sensations like shapes, colors, and tones, are used to label and categorize phenomena so that symbols can be manipulated, like when referring to someone by their name so you don't have to ensure that they are within sight and point at them every time they have to be taken into account.

The patterns and details that we notice, as opposed to the so-called random noise we ignore, is largely culturally-determined, including the idea of consciousness. People used to be convinced that Mars had canals because at the time digging huge gashes into the planets surface were all the rage so it was natural to think that a similar trend was occurring on a nearby world. I don't think that someone who grew up without language would ever come upon the concept of awareness on their own. What makes me more aware of anything than an infra-red sensor in a motion detector? Sure, I have more sensors for other things but I am deaf, dumb, and blind in the special case where automatic doors shine.

In filtering out static, we also make Type II errors, where we fail to see things that are physically there. Our optical blind spot is a good example—a black circle in the front of our visual field would reflect more accurately the reality of how we're configured within our environment but it doesn't help us figure out what we should be doing, so instead adjacent colors are just smeared over to remove that distraction. We often miss clearly visible things on the tip of our nose because we just assume that if we looked down at it while cross-eyed or one-eyed-shut, there wouldn't ever be anything worth seeing. As clear as we might like to think our experience of reality is, it's really just one big low-resolution impressionist mosaic of smears and dabs.

The questions you outline are very interesting, but there is another wrinkle to consider:

As sensation becomes perception (and perception becomes memory), is there any data lost or added?

In Beyond Good and Evil, Nietzsche uses several examples to highlight the point:

When you are reading a book (or a TED conversation prompt), how many of the individual syllables are skimmed over or guessed at? How many words do you fail to actually read and process? Psychology experiments have since shown that as long as the first and last letter of a word is unchagend, the middle can be compeletly altered wihtuot our comprehension being hindered. Is this because we recognize the mispellings individually and correct them or because our mind is actively projecting previous experiences (known words) into similar circumstances (similar spelling)?

Also, what do you see when you hear the word 'tree'? Chances are, the image you see does not match any known tree on Earth. Your mental image approximates not one, but all trees, and thus has essentially lost the base components and characteristics that would represent an actual tree. (If the tree/visual analogy isn't up to par, imagine the same but apply it to someone's voice and auditory perception/conception).

And if our own experiences/sensations only approximate reality, then how can we possibly know if this reducing mechanism worked exactly the same with another person? We are speculating. And hoping. And filling in the blanks with words we are all comfortable with. But just because I am familiar with the word 'blue' does not make me any more familiar with your idea of it or your experience with it.

I should note that I am not saying that we are incapable of experiencing similar phenomena, only that communicating what we experience does not transfer the experience itself and is thus subject to falsification of translation and perception.

thanks for putting an example of what you're talking about with 'unchagend,' =].

what youre saying also speaks to what I wrote in response to pratyeka's comment, that language is an agreement and by realizing that, we also must aknowledge that that agreement might be sticky, because we experience our side of the agreement in a totally self-centered way, that is, that our understanding of our side of the agreement of what a word in a language means is only, and CAN only be, solely informed by our own experience, biology, memories, etc...

Most will see 'unchagend", the phrase promoting the idea ends on that word. But having 'caught' that one, the reader immediately resumes reading normally and begins to fill in the middle of the word subconsciously, to the point that they do not even realize the other two examples in the very same sentence. It is interesting.

What is more interesting is extrapolating from there. You fill in the words because you are familiar with those words. What do you do in other familiar situations, like driving home from work or watching TV? Do you 'fill in the middle' here as well? How much of life do we miss, because we automatically use other parts of life as reference (and perhaps substitute)?

With a word, the beginning and ending are easily defined as the first and last letter. But experiences are more complex (right?).

Feb 15 2012:
One of my favorite topics. In the past 7 yrs or so I have become enthralled with the quest for what I call Absolute Truth, that is the Truth the way it really is despite our perception of it, i.e. Personal Truth.

What this has led to is the visualization of Truth as something like that of a diamond with multiple facets. Each one of us can see a limited number of facets at a time and often from unique angles, thus the Truth looks slightly different to each of us, even if we see many of the same facets.

When thinking this way, what ends up is that knowledge, (the Personal truth(s) concerning what we think and feel about an idea, thing, or event), becomes like a billion bright stars within the minds-eye, and the more we work to understand the different perspectives, the more magnificent it becomes.

So whether it is discussing the real shade of blue, who is the best team, or "how to effectively manage a nation of individuals that all have unique perspectives while encouraging the prosperity of all", it is clear that the moment we become concrete in our belief system, is the moment we stop growing.

Until we can communicate with thought that conveys emotion, we will never really "know" what others are sensing and even then it would be slightly influenced by our own perceived reality.

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"How charming it is that we have words and tones; are not words and tones rainbows and illusory bridges between things eternally separate?
To each souls belongs another world: to each soul every other soul is a back-world.
Among things most alike, the resemblance decieves us most delightfully, for the smallest gap is the most difficult to bridge.
For me -- how could there be an outside of me? There is no outside! But we forget upon hearing tones. How delightful it is that we forget!...
It is a beautiful folly, speaking: with it, man dances over everything."

-Nietzsche, Thus Spoke Zarathustra

SEP

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You're pointing out an interesting characteristic of language, which is that it is a contract-- that is, we all agree on the meaning of a word. The reason the question of 'are you saying the same blue as i am' is interesting is because of the solipsism of perception and even the solipsism of language-- that no one can know what an individual perceives or believes to be true. That's true even if there is something blue and two people both agree that it is blue, the language is lose in the sense that the language does not really prove that we mean the same thing by blue

I agree that in terms of the conversational dynamic, subconscious mental activity is irrelevant.

I was just pointing out (and letting Nietzsche speak for me) that in terms of subconscious mental activity, language is irrelevant, as it is a veil that cloaks true understanding as well as misunderstanding.

I don't think that's really true. The spectral characteristics of light reflecting off an object are independent of our perception, but how that spectral distribution of light gets turned into a color is 100% perception. Maybe a better way to ask Sophie's question would be: what does color look like to tetrachromat (eyes with four types of cones)? Can we ever communicate this or understand what the world looks like through senses that are different from our own?

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Feb 16 2012:
"The source of the "blue" is independent of our perception of it because if I'm not present, the source of the blue is still there, independent from my existence."

The source of color may be there, but there is no color without the perceiver. Color happens inside the head. Without our perception, the only thing you can measure is the wavelength and power of the light. That is NOT color—it is watts and nanometers. Color doesn't happen until it is perceived. This is why if you want to transform measurements taken from a spectrophotometer (i.e. watts and nanometers) into a color specification you need subjective data taken from actual observers. (For most color science this is in the form of the CIE standard observer data).

Basically, everyone has different densities of photoreceptors in the retina yet we all perceive color the same way (read their paper to see how they confirm this). In the experiment, the subjects' color perception was also shifted by wearing tinted lenses and in time they would feel as if wearing the tinted lenses was normal and without them the colors seemed off. This suggested to the researchers that we have some sort of built-in auto calibration for color in our brains.

As for whether we perceive color the same way among different people in terms of culture (the way we describe it, the way we associate it with other things) I would have to say yes. Although it's harder to show a complex relation between stimuli and what we consider as "sentient" thoughts, keep in mind, we do not perceive colors as stimulus in discrete color channels, in fact we can't experience colors individually. We experience colors in pair, and our brain relies on the lack of color simuli to perceive color. This system in itself is complex, yet we happen to evolve in a way where we can say for certain, blue is blue; and if you believe the paper mentioned above, the ability to agree on the color blue is calibrated, meaning, we all go through similar calibration and synchronization processes in order to be in agreement. If that is the case, then can we not extend this belief and say that in order for language to have evolved, we needed to have some built in way of synchronizing all of our perception in order to be able to communicate?

Feb 17 2012:
Colour perception varies with culture and the environment. In Amazonia people perceives different kinds of green, because there's green all around. In Antarctica, they perceive a lot of white tones because, once again, they are surrounded by that colour. And they have the words to name them.

Not everyone can distinguish between orange and red, for example. The perception of colour has many variants: culture, environment, our eyes and brain, light conditions, etc

Feb 17 2012:
I think at the root, the question is whether a person's perception is exactly the same if he/she has experienced the same exact stimuli (so if they were brought up in the same culture, in the same environment, etc).

As the paper I've referenced has shown, people are capable of calibrating their internal references to colors. We cannot know for sure whether people not from Antarctica can perceive a lot of white tones if they were transplanted in Antarctica and given time to adjust. We need to test this out through experimentation before we can make conclusions. I believe they will auto-calibrate their color scale in order to perceive those slight variations in tones. If that's the case, then can we not make the conclusion that if people were placed in the same situations, they should be able to calibrate their perception such that it's the same as each other?

Feb 22 2012:
My comment below suggested that we naturally relate our perception to events in the real world - real events such as being in a dark room or having our optic nerve cut affect our vision. It is now generally assumed that ALL details of our perception can be related to mechanisms/events in the real.
We confront the mind-body problem in this understanding if we try to superimpose the experience of seeing something with the mechanism by which we suppose this seeing to occur. The problem is solved easily - quite simply, both are expressed in terms of our own perception: - we invariably get a mind body problem if we try to insert our experience as an entity into the real world (which is itself expressed in terms of our own perception). The mind body problem amounts to trying to put experience into itself.

If perception is about mechanism then we naturally suppose that if we replace the mechanism a tiny piece at a time we could theoretically replace the entire mechanism without altering perception. But we understand that the body itself actually does this at least to some extent. Whether parts can be replaced by different materials is moot - it is doubtful that a silicon based perceiver could be equivalent to a carbon based one.

Can we integrate mechanisms to experience as others experience? One would expect that it depends on how modular the perception is. I would guess that seeing something as I do and then seeing it as you do is NOT like looking from one painting to another. Our visual perception is vastly more complex than the immediate electromagnetic input. I would guess that a mechanism that is capable of remembering and comparing two sets of visual experience is vastly more complex than what we ourselves possess. I would guess that this problem of comparison applies even to ourselves from a time significantly in the past i.e. our identity is recognizable (to ourselves and others) only because it does not change very quickly (an issue related also to mechanism).

Feb 21 2012:
The brain is dependent on biological nuts and bolts, wires and circuits... One day we can know EXACTLY how someone is thinking, why and what - even see through their eyes, because what the mind is made up of is a system... Are you asking what that would take to explore another mind OR are you just asking is it possible to do so?

No it is not possible but I read plenty of studies and journals that are examining these phenomena of sensory awareness.... Groupthinking is the best example.

Cool videos on youtube: Eyeborg - about cyborgs living today

As far as what it would take to get to this point of understanding the brain... That I am still figuring out myself.

Feb 21 2012:
The faculty of seeing isn't located in the body and any person (living being) is seeing from that same faculty.
Therefore every person sees the same within the limits of its personal development.
You can see in your dream, some people can see visions and it can happen that you see through the sensory organs of another body/person.

I know that the common notion is another one and for that reason not very productive. The way we vision the world is developed over the span of our evolution in relation to our needs for safety and food finding and differs among species in accord with their sensory organs. The imagery that tell us what we see are present to be evoked as we actually make contact with the corresponding code our senses perceive. So our nervous system has a role to play, not to generate our vision but in mediating between the object which is a fraction of the subject which is the center we all share.

Feb 21 2012:
Sorry, Frans. There's no reply button on your reply.
So, this reply is for your previous comment.
"It is seen with chimps in the wild that the young eat what mother give them. The first taste of any leave or fruit is tasty as it comes from the mother. When not it taste nasty."
"Impressions also are associated with emotions. A bad emotion provoked with an event associated to a color, word or taste can be revived any time the same color and the like appear."

Great point! I agree and love the way you explain it.

"It is natural to return to the trees with the delicious fruit and to avoid the snakebite by following our emotional memory."

Emotional memory....is it related to experiences?
But I think it’s because every creature has a basic instinct.
You know, an instinct for survival, something like that.
Or what you mean is that instinct is also related to emotional experiences?
I hope you answer for this question because I'm really curious about it.

Feb 21 2012:
I belive the percpetion of how others sense the world, is soley of their own. We may share ideas, strikingly similar to another, and yet maintain our own intellectual input/output not 100% same as other. Interesting indeed, and also opens the question of color being a learned behavior as well. Is the color blue a reality? Depth perception on colours based on photoceptors, seems somewhat unrealistic also, when we observe in the terms of "black/light". As mentioned before, when covering the shade of blue with black, blue does not exist. Just as, a pair of drapes, to change the appearance would be to withdraw or apply. A child completely visually imapired at birth, would be an example of attempted teaching to colors through smellng, tasting, touching, or hearing. Again, a child completely vision and hearing impaired at birth, would be an example of attempted teaching of colours through smelling, tasting, and touching. When we observe the way of coulor perception using the example of blind, and deaf, do we not have to also, need to acknowledge "speed" of scent? application of the scent to the taste buds? ect. ect. ect. Optical illusion is huge, as our own body of object has an application of bioelectricity. Thus raising a vast variety of questions of our own depth, and reflections...I would have to say we really cannot know precisely how another percieves, we have ideas only. Awesome question, thank you.

sensory perceptions, consciousness and subconsciousness, emotions...It's interesting how other factors play into such a question: How can we actually 'feel' another person's perceptions?

As some have stated, why would it matter- what joy or pain would that give us? And, if we felt anything at all (I doubt we won't) from "knowing exactly" how they felt in direct response to "what we actually felt"-- why should that do anything to us, according to the reality which we currently live all the while "apart" from knowing that possible experience? If we do 'feel' or 'sense' or even display the exact quintessence of their experience- should we say that we are now "them"? Or-- have we then engaged in some form of transcendental embodiment- in which we have or (possibly have) "become" greater than their actual being? such a question (and series of questions apt-to-be following) dictate that this question of the "'possibilities' of inter-subjective perception" is no longer in the realm of biology (as is asked)--- as biology is (if I'm correct)- strictly related to the applicable science of observable knowledge of living organisms. Am I right,

Now... to answer (or presumably tackle) the first part of this series of seemingly unruly and somewhat meagerly-apt-to-be-justified probabilities (if they are not just questions, that is)- (in part, does it bring pain or joy): if pain or joy is (shall we say- variables of the two most extreme emotions)- why should we search for these extremes just to prove to ourselves the (currently doubtful) chance of our beings being given to another being's sensory perceptions? and for what--- a greater realization of self? is there such a belief, if the axiomatic response is discreetly directed towards the already standardized, and controlled reality that we currently live in?? Thereby, I'm saying, it is all very interesting, but there are other factors which downplay the endeavor.

Feb 20 2012:
Agreeing on the principle of 80% identical (though that number may be a guess, I'm inclined to think that our brains and sensors are (on average) even more similar)

Our perception arises from external information and memory (in a constant loop).
And our perception of the world is therefore a representation. (As for how color and flavor coding goes... it gives us the ability to differentiate and respond in biological apt ways).

when applying correspondence theory of truth,
one can make estimates of the truth value of your inner representation (of the world, cosmos,...). It will never be a 100% correspondence, but we can see probabilistic differences (50% vs 80% vs 95% correspondence is quite different).

So can we know what another person senses? we can be quite sure about it (i.e. 60%+) but never completely sure.

And we are constantly advancing and querying these questions (psychology, neuroscience, biology,..), so we can come up with a high likelihood that blue is blue us blue across humans (and maybe some animals, and except the color-blind)

And as for trusting our senses: it is good to know they are very reliable, but still prone to illusions.

Feb 19 2012:
Your question is inspiring, Sophie - I just had the idea to re-phrase your question:
"How do I know that the person I see is the same person you see?"

During my last three years in the Ruhr Region I worked in many cities with a large migrant population - at least for Germany - of 20 - 30% of the inhabitants. You learn quickly that you have totally different views on reality: Blue is never ever blue.

So we - the European Capital of Culture - startet a film project where former migrants talk about their lives - and home: the old home they left and the new home they won. And of course now they are not at home in the old sphere they left.... blue in between blue? Understanding perception in this case is not only an intellectual matter, it decided over social peace or urban conflicts.

I'm further intrigued by the hard neurosciences trajectory of this thread. To expand on the concept of nurture, while sensory exposure in the early years allows those crucial senses to develop (and vice versa), it springs from one element of perceptual selectivity. I am constantly receiving sensory input from my body, but my brain has to work to determine what is relevant to my awareness. As such, even if we take in the same images, the same colours, textures, contrast, movement and so on as sensory input, an enormous deal of it may not make the VIP list into our consciousness (so to speak) and that selection process vary will in many ways, depending on genetic predisposition and environmental exposure.

Further, it pays to consider mental priming. If you, my closest friend and I are having a conversation together, I will likely be able to "read" her better. So, while we sense the same things in terms of wavelengths, light level etc., I will be more perceptually aware of her through experience, and thus will actually "see" more. In a different example, those being robbed at gunpoint typically give very poor descriptions of the suspect - often because all they were really looking at was the gun.

I believe that this trust you mentioned is our perpetually evolving schema of what it is to be a person. I can only see your world through my window of experience, and thus can only relate to you through my terms. Think of it like speaking two perceptual languages. How much gets lost in translation, then, is anyone's guess.

Feb 20 2012:
Hi Aldan. You said "I can only see your world through my window of experience, and thus can only relate to you through my terms. "
Perhaps you can only understand another's 'inner world' or emotional world or conceptual world' based on your own experience, but there is an overlap of shared external reality as well as a collegial agreement about reality that mitigate or minimize our misunderstanding of reality in the larger context. There are innumerable "terms of agreement" that enable and encourage understating between people. For example Helen Keller would not have been able to understand our reality if it was not also her reality, regardless of perception.

Feb 19 2012:
For the moment, the answer is no. We cannot know that we perceive the world similarly or differently, we can only conjecture based on the (dis)similarity of observations made by various individuals. However, we do know that experiencing similar events in different ways will often have the effect of causing a person to be less subjective about the way they and others react to said stimuli. But even the most objectively driven minds will have difficulty understanding the views of another when they don't have the requisite knowledge and/or experience.

When science has advanced to the point where we understand how the brain is constructed, we could theoretically modify some of the brain's circuits, thus solving this dilemma. The medium itself is completely different, but the actions performed would be similar to swapping out IC chips on a motherboard. If you can figure out which chips should be substituted where, it is possible that the motherboard would still function the same, even though the chips chosen might be completely different. Since the brain is more fault tolerant than a motherboard, you should also be able to swap in a set of circuits which are functionally similar, but ultimately different. After the brain has adapted to the new input and output created by the modified function, you might see things from a different perspective.

You could use this knowledge to change how a person's brain processes information, thereby bridging the understanding gap without subjecting a person to the events which created the circuitry in question. For example, you could make a petty thief decide on their own that stealing is wrong; just modify the circuits related to theft, and make them feel revulsion rather than enjoyment. However, abuse of such a technology carries equally weighty implications, which makes understanding the human brain a dangerous endeavor. If negative modifications could be easily scaled and propagated, the result might be worse than an atom bomb.

Feb 19 2012:
From skimming this page I see that most people took the stance that we can never know how another person senses the world. However, I don't see how we can be so sure that this is impossible: We can never actually know the extent of our knowledge. For example, in the middle ages, who would have thought that we could actually travel to the moon or sequence our own DNA? My assumption is very few, if any. Expansion of knowledge is hypothetically limitless.
We sense things only because a certain number of parameters exist in our bodies - our nervous system, more precisely - and the cells in this system react in generally the same way from human to human. Let's not forget that the DNA across humans is actually very similar. Furthermore it is actually very similar to the DNA of other organisms.
I would say that we do have the ability to perceive the world as another person does; for example, what if some day we could take a machine like an EEG and connect it between two people, causing the electrical impulses to travel between the two people. I am positive that this achievement would be extremely difficult, but I am not at all convinced that it is impossible.

In this video, Sheila talks about the signals produced by the retina, and how new technology has been developed that actually mimics these signals and transmits them to the brain, so that people with deteriorating retinas can effectively see.

For the question at hand, this is very encouraging. While complex at its own level, the solution seems simple -- we just need to determine where in the brain our senses are and where our perceptions are formed, and how we can interact with these parts.

The dangers of this, as Timothy James has pointed out, however, are numerous. With the the power to change how someone perceives something comes a bunch of ethical responsibilities. Suppose someone didn't like eating their vegetables - all we would have to do is implement our findings and change their perception: vegetables taste good, not bad. Alright so maybe that wasn't so bad. But imagine the exploitation of such power in the military, that's where things can get scary.

In my opinion, I don't think this is a road we should travel. To be able to alter someone's perception like that seems inhumane. By doing so, we remove identity. People would not be themselves, but who we want them to be. While I believe it can be possible to see how another senses the world, I don't think we should go about finding out how because the results could be more harmful than beneficial.

Feb 20 2012:
I agree with you that this technology could be incredibly dangerous. In a recent practice debate at school we discussed whether the technology used in Inception would be moral or not. The ultimate conclusion was that the human mind is above all else because it is the only thing that we can keep entirely to ourselves. Of course, Maslow's Hierarchy of Needs places physiological needs first but that is beside the point that the privacy of the mind should not be violated.
If used for the purposes of gaining information, then yes, I certainly agree that this technology is a bad idea. However, if used to achieve a greater sense of understanding between humans… well, that could be a very good thing. We have to consider which of the options outweighs the others, taking particular notice to whether the dangers justify the possible good.

Feb 21 2012:
Andrew,
i definitely agree with you that the knowledge to understand human perception is within our grasp given enough time. Sheila Nirenberg's talk about prosthetic eyes to repair retinas was mind blowing. It's incredible to imagine having the ability to recreate the complexity of visual perception.
While, yes, such science could lead to dangers, can't all realms of science? We can't hinder scientific progress and discovery because we're scared of how people might abuse it. There will always be those who try to exploit technology for their own personal gain, and it is up to us as a society to protect the purity of science and use it only for good.

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Feb 21 2012:
Although much more understanding about how another person visualizes and senses the world will become available to us in the future, I think that we have a huge overlap even now. As the video linked above shows in talking about the prosthetic eye, if we understand the code or the language of the brain from one person, things suddenly become possible that weren’t possible before (making the blind see). We already know that in the “normal” or average range of emotion, certain events will elicit the same response, meaning that we sense (whether it is seeing or hearing or smelling, etc) the same things to a close degree. We shouldn’t discount that our being social creatures mean that we have this amazing capacity to relate and understand one another. You could sum it up in the word empathy, which is a product of the senses and allows another person to feel what others are feeling and express it back to them. As people have said, this understanding will undoubtedly increase in the future, but we already have a base from which we do start.

Feb 21 2012:
I agree with the general sentiment that for the most part we as human beings do sense the world in the same way. If we didn't, projects such as the prosthetic eye would not work as they would have to be tuned to each individual user. I believe that this similarity is due to the fact that one can think of each cell as an individual sensor which either fires and is thereby encoded and later interpreted in the brain or not. The similarity in this process between individuals is understandable (due to the overlap in genetic code) which would lead to the conclusion that people sense the word in the same way. However, the question I have always had and I think is implied here is about the perception of the world, the way in which the combined signal in its entirety is created, interpreted and perceived. This I believe must be different from person to person because otherwise we would all be great at sports with terrific hand eye coordination, or artists with a sense for color and lighting in a painting or wine connoisseurs with the ability to sense hints of different ingredients. Since this is not the case to me it must be that while individual cells may very well "sense" using the same mechanisms the collection of these senses is different from person to person making up a varied view of the world. Color blindness I feel is just an obvious example of how people do indeed perceive the world in different ways suggesting to me that likely the sky is slightly different shades of blue to different people.

Feb 19 2012:
I think the answer is that while not everyone will perceive and interpret things the same way, a lot of people do. I have a form of synaesthesia where I can taste colours in my food (eg, lemons are green to me, most fish is blue). I also frequently see the letter "y" as a deep purple. I find it odd, because I've never been able to find a case taste-colour synaesthesia online, yet my mother has the exact same one as me. She even interprets the same colours from the same foods that I do.
So having never found a case similar to mine on the internet, I'm drawn to the conclusion that I am very unique in the way my world is compared to yours, even if it's unique in a minor way. At the same time though, my mother having the same synaesthesia shows me that as unique as it is, her visual blue is probably the same as my visual blue based solely on the fact that her tasted blue is the same as mine.

Feb 18 2012:
I love this question.
It may not be helpful at all, but for me, we can never know exactly how another person sense the world.
For example, remember when you first tasted Sushi?
When I first tasted it, it was just okay. But for my father, he said that it was really, really delicious.
As time went by, I've been getting familiar to the taste of sushi, and nowadays, when I eat sushi, I can really enjoy the taste of it.
The taste of sushi can vary depending on the people who taste it.
And the way you sense the world even can change as time goes by.

All we can do is just guessing people's mind according to scientific methods and experiments.

Let me give you another example for understanding.

When I see the green color of my album, I feel comfortable.
I sense the color as a humble and familiar thing.
But for my friend, she said that it looked ugly.
I think she senses it as a dull color as long as all she’s talking about exactly reflects her “sense”.
So, all I can do is just trying to feel the same way—which can also not be exactly same as her feelings.

Anyway, there’s no scientific proof for my opinion.
So, feel free to disagree with it and give me any suggestion so that I can learn more about this question.

I think that your example is actually an excellent addition to this conversation in the context of the previous comments. There are two different ways in which we can think about the senses (taste, for example) – the “scientific” and the “psychological.” From the scientific viewpoint, all human beings sense in “approximately” the same way. There is an excellent TED talk by Sheila Nirenberg dealing with the senses from the scientific standpoint (http://www.ted.com/talks/sheila_nirenberg_a_prosthetic_eye_to_treat_blindness.html). To the scientist, the senses are nothing more than sequences of code that are sent to the brain as electrical signals. When looking at the senses as mere decoding systems for electrical signals, it is plausible to assume that the senses are not too different from one person to the next. However, if we look at the senses from the psychological viewpoint (as you have done), senses change, not only from one person to the next, but also with time. The way that our brain interprets a “sense signal” is based on our history and experiences. For example, your opinion of sushi changed over the years, thus changing the way sushi tastes to you.

Feb 21 2012:
Thank you for your reply Veronica:)
Your comment is thought-provoking and very interesting!
But what if the reason why the taste of sushi can be different from person to person is because of some hereditary factors? Take my dad and brother, for example, they do not like pork(not hate but) since they say it tastes too greasy. They believe that it’s because of my granpa who also didn’t like pork. My dad thinks it must be genetic. If it’s true, then, we can’t be sure that it’s because of psychological or historical factors.

Since I’m not a scientist I’m not sure if I’m right, please correct me if I’m wrong about this.
I really want to learn more about this.
Best,
Elizabeth

Feb 21 2012:
Perceiving is one thing, to distract any meaning from it is another.

It is seen with chimps in the wild that the young eat what mother give them. The first taste of any leaf or fruit is tasty as it comes from the mother. When not it taste nasty. So it happens that among groups there exist cultural differences. Apes from one group that eat a kind of leaf that another group never will touch. With human beings it isn't much different.
Impressions also are associated with emotions. A bad emotion provoked with an event associated to a color, word or taste can be revived any time the same color and the like appear.
It is natural to return to the trees with the delicious fruit and to avoid the snakebite by following our emotional memory.

I'm also not much of an expert when it comes to the senses. However, at first glance, it seems that what you're referring to as a hereditary sense could be grouped together with what I referred to as the psychological. Perhaps, if a person grows up hearing that a certain food is not tasty, he or she will develop a subconscious prejudice against that food. Then, his or her brain might interpret the taste of that food as unpleasant - not because of genetics, but because of memories and experiences.

Feb 18 2012:
What if it isn't important if two people perceive two things the same way, but rather that they perceive the difference between two things the same way?

What I mean to say is that it isn't important if my shade of indigo looks the same as your shade of indigo - what is important, however, is that we both sense the same difference between indigo and blue, which is a product of the physical nature of those colors.

Additionally, we may not even call two colors the same way, or we may split them up into different categories. Some cultures have only three commonly used color words in their language, whereas some have additional words for certain shades of colors. Even though one may be more sensitive to these difference in experiments, it has been shown empirically that all people are still able to tell the differences between two colors.

Finally, I'd like to point out that there are many similarities between the mapping of outside sensory stimuli on regions of the brain across individuals. However, the brain exhibits a lot of plasticity, and many differences between people, so certainly there should exist variability among individuals. Until the regions directly implicated with perception are identified and studied, we may not know if these physical differences actually result in different perception.

My point still remains, however: It is not the perception of point A and of point B that is the same between people; rather, it is the difference between point A and point B that we are all able to perceive similarly. Thus, it doesn't matter if we all see all colors differently because we still have the same perception of them relative to one another!

Perhaps this logic can be extrapolated to all sensory systems.

Any thoughts?
I'm anticipating that color-blindness may be a counter-argument to my claim, but I don't know enough about its neurological basis to comment on it at the moment.

One thing I have noticed throughout the conversation is that some people comment on the interpretation of sensory perception, while others are commenting on strict perception-- that is, how we see brightness or color, not how we interpret color. I replied to some people who responded in the vein of the former, saying that it is easy to argue that interpretation of sensory perceptions are different between two people, but that we are trying to talk about something more difficult to ascertain-- sensory perception itself and how that might be different. It's a nuanced thing, but it helps to think of it on a time scale-- FIRST we perceive a stimuli (usually filter it with our sensory organs and the brain puts together the perception), and only THEN does our brain take the time to 'think'-- that is, to interpret what it saw, to form an opinion, etc.

I'd like to draw everyone's attention to a comment made by Marina Najdoska. Marina highlights an interesting point, which is that maybe there is memory in sensory perception. This leads to another question: if I have seen the same exact blue over and over again,and you have seen it just now for the first time, which our perceptions be different because I've seen it before. Likely our conscious or subconscious mind is at work to help us form an interpretation of the stimuli, but will we literally see the stimuli differently if we've seen it before?

Consider neural adaptation, when our senses respond differently over time to a stimulus that is constant. This is similar except rather than the stimuli being constant, the stimuli has popped up in our lifetime numerous times

Feb 18 2012:
No 2 things are exactly the same - even mechanically (and precisely) produced things have utmost minute variations from each other. In that case, can we ever know how other person "senses" the world - if you are asking most exactly and precisely, of course not. Can we know how other person most likely senses the word - the answer is yes depending on one's level of perception, sensitivity etc. Books, conversations, movies, expressions - gives some insights into how one is sensing the world.
Why is it important to answer this question?

Feb 18 2012:
No Sophie - we can never know how another person senses the world. And isn´t this a great luck?

Image we all could sense the same blue - and everybody knows from the other that he senses the same blue. Where is the thrill of communication?

Communication is about narrowing the gap of the different - just a love is not about finding the same or a second me, but a different which is affect to me.

So let us enjoy the differences of perception to learn about realiy and its many dimension and sides. a puzzle.
The only thing missing now is safety and security that understanding is possible. .... this feels not so good, but historically we must admit that despite constant misunderstanding ( be it on society level (war) and or personal level (divorce) ) mankind still progresses... a least that is my reality.... smile.

great comment. if you're interested, read the rest of the conversation and you'll read about similar ideas about language and communication, its limitations, and the answer to a question someone asked to the effect of 'why am i asking this question?'

the answer was essentially the last thing you said-- that humans are essentially lonely beings, which makes connecting to other people so vital, which is why we are interested in confirming our life experience by understanding how others experience it

If I reflect on how we connect I was brought up and raised in school & university with the idea that connecting & communication is verbal & is about exchange of knowledge and information. Now after 30 years in profession and experience I believe it is most of all non-verbal communication we connect by.

In my professional field of urban change I experience that art and culture are sometimes even transmitters and mediators which are absolutely necessary for urban progress -since verbal and non-verbal communication often breaks down between the special interests groups in cities. often verbal communication is an endless loop of mis-perceptions and prejuidices within the city - the outsider view of an artist is the distraction out of the vicious cycle - or into new options to act.

I wonder if you have similar experiences in our association on art & science?

Feb 18 2012:
From my perspective, this is one of the fundamental reasons why communication is such an important area of study. In traditional, functional models of communication (those that are most commonly adopted in business contexts and in popular cultural contexts), communication is merely expressing your viewpoint articulately. Communication is much, much more than that.

Dialogic communication, or dialogue, is the process by which individuals come together to create new meaning. In other words, each communicator comes into the interaction with their own percpetions grounded in their own experiences and positionality within the social context in which they exist. Their social positioning impacts the way they perceive the world, and this impacts their approach to communicative interactions. In other words, their perspective is uniquely shaped by their identities and how those identities are perceived within a specific historical and social context. All of this shapes the way they perceive the world.

Contrary to popular ideas about communication, rather than seeking to impose a particular perspective, dialogue would prescribe that individuals seek to not only understand one another's perspective, but then be open to how all perspectives involved in the exchange will influence the meaning that emerges between the communicators. We are not attempting to compete with one another to have our perceptions of the world accepted as preferable...we are simply attempting to share our perceptions and remain open to others so we can negotiate a sense of shared perception that emerges from our communication about individual perception.

It's discussions like these that remind us of what communication is really supposed to be about--opening us up the the world around us rather than imposing our perspective on the world around us.

Feb 18 2012:
What you say about how dialogic communication brings new meaning is definitely true-- also makes me wonder if attempting to communicate how someone experiences a perception might affect the perception due to power of suggestion...yout hink the blue looks like a royal blue and your friend says i think that's actually because it might be a shade of indigo, next time you look at that blue it may look different...